Post mortem findings

Findings are variable and non-specific. Depending on the strain of virus, the host species, the severity of infection and when during the course of infection the bird is examined, findings may include: on the head, facial oedema (fluid under the skin making the face appear swollen), inflammation of the tissues of the eyes; in the respiratory tract, congestion (reddening, swelling of blood vessels) of the windpipe (trachea), haemorrhages, and thickening of the air sacs, with mucous or caseous (cheesy) material on the air sac surfaces; in the gastro-intestinal tract, haemorrhages and or necrotic lesions; in the kidneys, (often no visible lesions, but microscopically nonsuppurative nephritis and foci of renal tubule necrosis); in the reproductive tract, haemorrhage and discolouration, ovarian follicles on the ovaries collapsed (flaccid), sometimes egg yolk in the abdomen; the spleen may be necrotic. In the CNS (brain and spinal cord) there are no visible lesions, but microscopically there is a non-suppurative encephalomyelitis (inflammation of the brain and spinal cord, without pus formation). Microscopic lesions also can be found in the lymphoid tissues and liver (small points of necrosis).

Affected double-crested cormorants were found to have a characteristic non-suppurative encephalomyelitis. Lesions, often found in discrete foci (points in the tissues), included “neuronal necrosis, spongy change, gliosis, perivascular infiltration with mononuclear cells, endothelial hypertrophy, and hemorrhage”; sometimes there was only perivascular mononuclear cell infiltration and endothelial hypertrophy (Kuiken et al., 1999). In pigeons, the viscera are generally congested and the kidneys, spleen and pancreas may appear mottled. In ostriches, oedema of the head is a common finding.

Diagnosis

Because none of the findings or combinations of findings from clinical examination or at post mortem examination are pathognomonic (characteristic of this disease, and this disease only), it is necessary to use microscopic lesions together with isolation of the virus to make a definite diagnosis. Due to the range of clinical signs and necropsy findings, differential diagnoses include other diseases causing gut, respiratory and/or nervous signs and lesions.

Serological tests can be used to demonstrate whether or not individual birds or populations of birds have been exposed to NDV.

Control – Vaccination and Biosecurity

There is no treatment for this disease once clinical signs have developed.

In birds which have been exposed to the virus but are not yet showing clinical signs, it is possible to treat with hyperimmune serum at 2 mL serum per kilogramme bodyweight of the bird (i.e. give them lots of antibodies to fight off the infection). However, nervous signs can occur despite the presence of antibodies (Gerlach, 1994).

Newcastle Disease may be prevented by vaccination. Different countries vary in whether they allow vaccination or indeed if it is compulsory. Requirements may vary between different bird groups – for example compulsory vaccination of racing pigeons and permission to vaccinate domestic chickens; vaccination appears unnecessary in waterfowl.

Both live attenuated vaccines and dead vaccines have been used. Dead (killed, inactivated) vaccines are given by injection, while live vaccines are given by dripping vaccine into the eyes of each bird or by giving the vaccine in drinking water. Injected vaccines are generally required except in poultry and related species (Galliformes - pheasants etc.).

Vaccines which are oil-adjuvanted (combined with oil to increase the immune response) must be used with care, as some birds may develop an abscess at the injection site (whether subcutaneous or intramuscular). It is generally recommended that live vaccines designed for domestic poultry should not be used in other species except in galliformes.

However, in ostriches live vaccines given as eye drops in two-week-old chicks, as well as inactivated vaccines, have been used; vaccines are used in ostriches at higher dose rates than in chickens (usually two to five or even ten-times the chicken dose) (Alexander, 2000).

In pigeons in the UK, vaccination is legally required for birds which are raced or exhibited (Harper, 1996).

In the event of an outbreak in domestic birds, the main control method used is slaughter of infected flocks, together with movement restrictions and strict biosecurity.

Biosecurity is also important to keep this disease out of bird collections. All new birds should be quarantined for at least 30 days on entry into your collection. If you visit another collection, protect both collections by wearing different clothes for the visit, not the same as those you wear while caring for your own birds—and change again when you return home. Risks of introduction by wild birds cannot be eliminated, but may be decreased by use of e.g. small-gauge netting, where practical, to prevent wild birds entering your aviaries; roofing, particularly above food containers (to reduce the risk of contamination with droppings from wild birds) and for birds in moor open enclosures, feeding methods which reduce food availability for wild birds and the risk of food contamination by wild birds’ droppings.